JP2568819B2 - Intermittent magnetic recording / reproducing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intermittent magnetic recording / reproducing apparatus for recording an audio signal on a long-term monitoring VTR mainly for crime prevention.

[Conventional technology]

Conventionally, an audio signal cannot be recorded in such an intermittent recording / reproduction VTR, and only a video signal is intermittently recorded in a frame (or field).

6 to 8 show the configuration of a conventional intermittent recording VTR.

In FIG. 6, (1) is a video amplifier for inputting a video signal from a television camera with a high input impedance.
(2) is a video signal recording circuit typified by an FM modulator that modulates a video signal into an FM signal, and (3) is a circuit for amplifying the FM signal and supplying a recording current to a video head for recording on a magnetic tape. (4) is a mode switching switch that switches video head input / output between recording mode and playback mode, and (5) is an FM demodulator that demodulates FM signals detected from magnetic tape during playback. Video signal playback circuit,
(6) an intermittent drive circuit for intermittently advancing the magnetic tape,
(100) is a rotary drum having two video heads V _R and V _L , (101) is a magnetic tape spirally attached and run over a predetermined range of the peripheral surface of the rotary drum (100), (10)
2) is a capstan shaft for advancing the magnetic tape (101), and (103) is a pinch roller which rotates while contacting the capstan shaft (102) with the magnetic tape (101).

Next, the operation will be described. Video signal amplifier (1),
FM via video signal recording circuit (2) and F signal amplifier (3)
The signalized video signal is applied to the video heads V _R and V _L on the rotating drum (100) via the mode switching switch (4). However, at this time, as shown in FIG. 7 (a), the television signal sent from the TV camera
_{V 0, V 1, ... V} 9, V 10, V 11, V 12, and is constituted ... sequentially contiguous with. In an intermittent recording / reproduction VTR, if these are continuously recorded, the consumption of the magnetic tape (101) is so large that the current model can record for only up to about 8 hours, for example, but as shown in FIG. 7 (c). For example, if you record every two fields out of 40 fields intermittently, And it is prolonged. In order to perform intermittent recording in this manner, the magnetic tape (101) is intermittently moved, and the video tracks recorded on the magnetic tape (101) intermittently are adjacent to each other with a slant as shown in FIG. There must be. For this purpose, an intermittent drive pulse signal is generated by an intermittent drive circuit (6) based on the vertical synchronizing signal, and the pulse signal is applied to a capstan motor drive circuit (not shown), and a capstan shaft (102) and a pinch roller ( The magnetic tape (101) is advanced exactly by the rotation of 103).

The above operation is performed on the video head on the rotating drum (100).
Written on the magnetic tape (101) by V _R and V _L ,
The head gap width of both V _R and V _L is 0.25μ, like general VTR.
This is a surface recording recorded only on the surface layer of the magnetic tape (101) as narrow as m.

During playback, the video heads V _R and V _L from the magnetic tape (101)
The detected FM signal is demodulated by a video signal reproducing circuit (5) to obtain a video signal.

[Problems to be solved by the invention]

Since the conventional VTR for intermittent recording / reproducing is configured so that the magnetic tape runs intermittently, it is not possible to record audio signals on the upper end (linear audio track) of the magnetic tape using a fixed head. Natsuta (Recording is not possible for about 0.63 seconds while the magnetic tape is stopped). Therefore, the conventional VTR for intermittent recording / reproduction has a problem in that recording of an audio signal is abandoned and the function is not provided, and information (voice) by sound at the time of a crime prevention accident cannot be obtained at all. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide an intermittent magnetic recording / reproducing apparatus capable of recording and reproducing an audio signal in an intermittent recording / reproducing VTR.

[Means for solving the problem]

An intermittent magnetic recording / reproducing apparatus according to the present invention is arranged such that a magnetic tape is intermittently run, and a video signal input during the run is inclined by a video head provided on a rotating drum with respect to a running direction of the magnetic tape. In an intermittent magnetic recording / reproducing apparatus that sequentially records on a surface layer adjacent to a track to be recorded,
A / D conversion means for converting an audio signal into a digital signal having a predetermined number of bits in order to record a continuously input audio signal at the time of intermittent recording of a video signal, Bit number conversion means for compressing the number of bits of a digital signal having a predetermined number of bits within a range that can be determined during reproduction, storage means for temporarily storing a digital signal output from the bit number conversion means, Correction code generation means for adding an error correction code to the digital signal stored in the means, and digital compression means for compressing the digital signal output from the correction code generation means on a time axis in accordance with the intermittent running of the magnetic tape And an audio head having a wider azimuth angle than the gap width of the video head, wherein the audio head provided on the rotating drum is provided. Using a Dio head, a compressed signal output from the digital compression means when the magnetic tape runs is converted into a deep layer of the track different from a surface layer of the track on which the video signal is surface-recorded in a thickness direction of the magnetic tape. This is to perform deep recording in a state of being superimposed on a part.

[Action]

An intermittent magnetic recording / reproducing apparatus according to the present invention converts a continuous audio signal into a digital signal having a predetermined number of bits, further compresses the number of bits, and adds the error-corrected signal to the signal having the reduced number of bits, The digital compression means compresses this signal on the time axis in accordance with the intermittent running of the magnetic tape, and records it deeply on the magnetic tape by the rotating head. The sound is played.

(Example of the invention)

In Fig. 1, (1) (2) (3) (4a) (5)
Each circuit of (6) is exactly the same as that of FIG. On the other hand, the audio signal is sent from the audio input terminal to the audio signal amplifier (21).
Is added to (22) is, for example, a 6-bit AD converter for converting an analog signal into a digital signal, (23) is a 6-4 converter for companding the number of quantization bits of 6 bits to, for example, 4 bits, and (24) is a correction. A correction code generation circuit for generating a code, (25) a time axis compression modulation circuit for compressing and modulating the time axis of a digital signal, and (26) a system clock signal generator for controlling a sequence for processing the audio signal. , (27) is a RAM circuit for temporarily storing the digital audio signal in order to add a correction code to the digital audio signal and further compress the time axis. (4b) is a mode switching switch for switching between a recording mode and a reproducing mode of an audio signal.
The configuration is the same as that of the video signal mode switch (4a). (28) is a reproducing circuit for demodulating a digitally-modulated signal, which performs almost the reverse operation of the recording operation. Therefore, the details are omitted by being represented by one block in the figure.

The operation of the embodiment will be described below with reference to FIGS.

First, the analog audio signal amplified by the audio signal amplifier (21) is converted into a digital signal by the AD converter (22) and quantized. In general, according to the sampling theorem in which a continuous analog signal is sampled at a certain time interval, the original waveform can be completely reproduced by sampling at a frequency twice or more the highest frequency of the spectrum distribution of the signal. Further, it is possible to identify an audio signal if its frequency characteristic is 10 KHz. Therefore, in this case, it is enough to sample at 20KHz (in the case of 20KHz, the reproduced audio signal is However, it is enough for the sound of a security VTR. The AD-converted 6-bit digital audio signal is converted from 6 bits to 4 bits by nonlinear quantization for hardware simplification.
Reduce the number of bits to bits. In general, bit compression reduces dynamic range and degrades sound quality, but four bits are sufficient for crime prevention. There are various types of correction codes for reducing the malfunction of the system. For example, it is desirable that a correction code is generated for each word, such as a parity check. Such a digital signal is temporally compressed to 1/20. In this case, the time axis compression modulation circuit (25) performs an operation of once writing the digital signal into the RAM at a predetermined speed and calling it at a high speed. For example, when the transmission rate of the data obtained from the 6-4 converter (23) is obtained, 20
KHz x 4bit = 80KBPS. Here, to compress the time axis to 1/20, it is necessary to call 80 KBPS data 20 times faster. That is, the data in the RAM is called at a high speed of 80 KBPS × 20 = 1.6 MBPS, and the time axis compression modulation circuit (25) uses, for example, Bi.
-Digital modulation using the phase modulation method, and further amplifying and passing through the mode switch (4b), the head for deep recording
It is added to V _R ′ and V _L ′ and recorded on a magnetic tape.

Now, as shown in FIG. 2 (a), the video signal from the television camera is sent out sequentially in the order of V ₀ , V ₁ ,... For each field on the basis of the vertical synchronizing signal. On the other hand, as shown in FIG. 2 (a '), the audio signal from the microphone or the like is A ₀ ,
A ₁ ,... Are sequentially sent out, but a continuous analog signal is sent without any particular reference signal. Here, FIG. 2 (a ') is named A ₀ , A ₁ ,. In a general continuous recording VTR, the magnetic tape runs at a constant speed, the video signal is sequentially recorded in the rotating video head in the diagonal direction as V ₀ , V ₁ , etc., and the audio signal is a fixed linear audio head at the top 1 mm of the tape. , A ₀ , A ₁ ,...

However, in the intermittent VTR, as described with reference to FIG. 7, the traveling speed of the magnetic tape is stepped as shown in FIG. 2 (b), and the field (or frame) of the video signal selected during this traveling period. ) Is recorded. Therefore, first, 0.667sec audio signals to A ₁₁ to A ₅₀ consecutive
The analog audio signal between them is converted into a digital signal as described above and time-compressed, as shown by the broken line in FIG. 2 (c ').
The audio signal stored in the RAM (27) has all information compressed in time. ).

On the other hand, the video signal only field of V _11, V ₁₂ of between 0.667sec until V ₁₁ ~V ₅₀ continuous, up to V ₅₁ ~V ₉₀ 0.66
Only fields of V _51, V ₅₂ is selected from among the inter-7 sec.

Rotation head V _R of the two signals _{respectively, V L, V R ',} V L' is added to. Here, the video signal is modulated with a frequency relationship as shown in FIG. 3 (a), and the audio signal is subjected to digital modulation at a frequency as shown in FIG. 3 (b). The heads V _R and V _L provided on the rotating drum (100) and corresponding to video signals have a small gap width g (0.25 μm).
m), the azimuth angle is ± 6 °. The heads V _R ′ and V _L ′ in charge of digital audio signals have a large gap width g ′ (1.0 μm) and an azimuth angle of ± 30 °.

Therefore, as shown in FIG.
Fig. (C ') A digital audio signal indicated by a broken line is used for a deep recording head.
V _R ', V _L' are recorded in, and then records the video signal of the field that has been selected over the surface recording head V _R, in V _L.
At this time, the heads V _R , V _L , V _R ′, and V _L ′ have different gap widths and different azimuth angles, so that interference is extremely small and there is no practical problem.

This state is shown in FIG. 4 and FIG. 5 when viewed from above the magnetic tape. In the state where the video signal and the audio signal are superimposed on the surface layer and the deep layer of different tracks in the thickness direction of the magnetic tape, respectively. That is, writing and recording are performed by one head.

In the above description, specific examples have been given and specific numerical values have been given, but the present invention is not limited to these numerical values. Various methods can be considered for compressing the time axis of the digital audio signal. The larger the compression, the larger the intermittent period can be selected. Also, the higher the frequency of the calling clock signal of the RAM, the larger the intermittent period can be selected. However, in this case, it should be noted that mutual interference is likely to occur because the frequency approaches the FM modulation frequency of the video signal.

The sound quality is slightly degraded because the number of bits is reduced and the time axis is compressed. To prevent this, a noise reduction circuit is provided before the audio signal amplifier (21) or the audio signal amplifier (21). It is also possible to improve the S / N ratio by inserting between the A / D converter and the AD converter (22). In the above description, the description of the reproduction circuits (5) and (28) is omitted, but the operation is the reverse of the recording operation.

〔The invention's effect〕

According to the intermittent magnetic recording / reproducing apparatus of the present invention, an analog audio signal continuously transmitted is digitally converted into a predetermined number of bits, and the number of bits is compressed to reduce the information amount of the signal, thereby correcting the error. After the sign is added, the digital signal is compressed on the time axis, and the digital signal is recorded in the deep part of the track of the magnetic tape. Since the video signal of the field (or frame) picked up is recorded on the surface layer, the sound is continuously reproduced at the time of the intermittent reproduction, and there is an effect that two information of the image and the sound can be provided.

In addition, the audio signal converted into a predetermined digital signal is provided with a bit number conversion means for compressing the number of bits within a range that can be discriminated at the time of reproduction. Since the number of digital signals is converted to digital signals and then the number of bits is further converted to further reduce the number of bits, the dynamic range of the audio signal when digitally converted to the first predetermined number of bits is used ( The reproducibility to an analog signal when converted by a predetermined number of bits can be ensured), so that the number of bits can be reduced. As compared with the case where the number of bits is converted, the deterioration due to the digital conversion of the audio signal can be suppressed. Further, by reducing the number of bits of the audio signal, the capacity of the storage means and the like can be reduced, and the hardware can be simplified.

In addition, the provision of the correction code generation means prevents malfunctions in the signal system due to the digitally converted audio signal, so that the audio signal can be accurately recorded and reproduced, and furthermore, the audio signal can be recorded on the time axis. It is possible to improve the S / N ratio at the time of compression and decompression at.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an intermittent magnetic recording / reproducing apparatus of the present invention, FIG. 2 is a time chart showing the operation of the embodiment of the present invention, and FIG. And FIG. 4 is a characteristic diagram showing the frequency relationship between deep recording and deep recording. FIG. 4 is a cross-sectional view of a magnetic tape on which surface recording and deep recording are performed according to an embodiment of the present invention. FIG. FIG. 6 is a block diagram showing a conventional intermittent magnetic recording / reproducing apparatus, FIG. 7 is a time chart showing the operation of the conventional apparatus, and FIG. 8 is a track chart of a magnetic tape of the conventional apparatus. It is. In the figure, (21) is an audio signal amplifier, (22) is an AD converter, (23) is a 6 → 4 converter, (24) is a correction code generation circuit, (25) is a time axis compression modulation circuit, (26) is a system clock signal generator, (27) is a RAM, (28) is an audio signal reproducing circuit, and (100) is a rotating drum. V _R ′, V _L ′
Is an audio head for deep recording and reproduction. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (2)

(57) [Claims] A magnetic tape is run intermittently, and a video signal input during the running is sequentially adjoined by a video head provided on a rotating drum to a track inclined with respect to the running direction of the magnetic tape. In an intermittent magnetic recording / reproducing apparatus that performs surface recording by means of an A / D converter, in order to record a continuously input audio signal at the time of intermittent recording of a video signal, AD conversion means for converting the audio signal into a digital signal having a predetermined bit number Bit number conversion means for compressing the number of bits of the digital signal having the predetermined number of bits output from the AD conversion means within a range that can be determined at the time of reproduction, and converting the digital signal output from the bit number conversion means Storage means for temporarily storing, correction code generation means for adding an error correction code to the digital signal stored in the storage means, and correction code generation means A digital compression means for compressing a digital signal output from the magnetic tape on a time axis in accordance with the intermittent running of the magnetic tape; and an audio head having a width wider than a gap width of the video head and having a different azimuth angle; Using the audio head provided on the magnetic tape, the compressed signal output from the digital compression means when the magnetic tape is running is compared with the surface layer of the track on which the video signal is surface-recorded in the thickness direction of the magnetic tape. An intermittent magnetic recording / reproducing apparatus, wherein deep recording is performed in a state of being superimposed on a deep part of a different track. 2. The intermittent digital compression means according to claim 1, wherein said digital compression means reproduces the digital signal stored in said storage means at a read speed higher than its write speed and performs digital modulation. Magnetic recording and reproducing device.